The present invention relates to radio communication systems, in particular systems employing a Frequency Division Duplex (FDD) scheme of frequency allocation, for example, a Global System for Mobile Communication (GSM) or a Universal Mobile Telecommunications System (UMTS).
In an FDD scheme, an first frequency band is allocated for uplink communications and a second frequency band is allocated for downlink communications between, for example, a mobile terminal and a fixed terminal, such as a base station.
A Code Division Multiple Access (CDMA) system operating in the FDD scheme, such as Wideband-CDMA, as has been proposed for UMTS has a limited capacity. The capacity is limited by interference. Therefore, as the system loading (the number of subscribers using the system) increases, the level of interference in the system increases, thereby limiting the capacity of the system.
It is therefore desirable to increase the capacity of a telecommunications system, such as a Wideband-CDMA system, operating under the FDD scheme in order to accommodate an increase in the demand for loading the telecommunications system.
According to a first aspect of the present invention, there is provided a method of improving capacity in a duplexing scheme, the duplexing scheme having a first band of frequencies and a second band of frequencies, the method comprising the steps of: determining an amount of available capacity on the first band of frequencies, transmitting, on the first band of frequencies, a variable amount of feedback data corresponding to the amount of available capacity on the first band of frequencies, the feedback data comprising data for improving the quality of communications on the second band of frequencies, and optimising transmissions on the second band of frequencies using, when available, the feedback data.
According to a second aspect of the present invention, there is provided an apparatus for improving capacity in a duplexing scheme, the duplexing scheme having a first band of frequencies and a second band of frequencies, comprising: means for determining an amount of available capacity on the first band of frequencies, means for transmitting, on the first band of frequencies, a variable amount of feedback data corresponding to the amount of available capacity on the first band of frequencies, the feedback data comprising data for improving the quality of communications on the second band of frequencies, and means for optimising transmissions on the second band of frequencies using, when available, the feedback data.
According to a third aspect of the present invention, there is provided a method of optimising transmit diversity in an antenna array, the antenna array comprising a plurality of antennas, the method comprising: selecting a predetermined number of antennas from the plurality of antennas, and setting the phase of each of the predetermined number of antennas in response to feedback data received from a terminal arranged to receive transmissions from the antenna array.
Other, preferred, features and advantages are set forth in and will become apparent from the accompanying description and dependent claims 2 to 11 and 14.
By using spare capacity available on the uplink band of frequencies to transmit feedback data, it is possible to optimise downlink communications to reduce interference in the downlink band of frequencies, thereby increasing downlink capacity.
Such a technique is particularly useful in situations of asymmetric system loading, for example, where the loading on the downlink is greater than on the uplink. Such loading may occur in locations where slow moving subscribers exist, such as in microcells and picocells.